lowest heat? or best light? if you want real low heat, go flourescent tubes (T5). Blacklights won't do shit.
(My opinion) You might be over feeding your plants, only water (nutr. mix) when the top soil is almost dry or every 4 days. If u see more leaves burning. Hps lights are very good. They are a little hot but work very well when they are put the right distance from the plant. Flo. wont give your plant the full potential. They are good for clones, and sprouting seeds.